1. Field of the Invention
This invention generally relates to information communicated in a digital wrapper and, more particularly, to a system and method for programming the criteria by which the loss of frame synchronization in a digitally wrapped-communication is defined.
2. Description of the Related Art
Frame synchronization is used in most communication technologies where extra bandwidth is required to add functionality into the original data stream. There is no standard practice with respect to the bandwidth allocation for frame synchronization words. Neither is there an ability to customize the use of that bandwidth and synchronization thresholding to adapt to various bit error rate conditions in a variable rate forward error correction (FEC) system implementing an interleaved multi-frame superframe.
It would increase information bandwidth if all the bytes, or words of a digital frame structure could be devoted to payload. However a significant portion of the frame is devoted to FEC to remove errors that are introduced in data transmission lines. Even fiber optic systems can be noisy enough to introduce errors, when the distance between nodes is great enough. In addition, part of the frame must be used for maintenance functions between communication nodes. Further, a portion of the frame must be devoted to synchronization. The synchronization function becomes even more critical when the frames are scrambled to randomize the data density. These maintenance and synchronization bytes reside in the overhead section of the frame. However, as mentioned above, there is no standard protocol defining the number, location, or value of frame synchronization bytes. Hardware devoted to any particular protocol or implementation quickly becomes obsolete. An exclusively software approach to managing communications is cumbersome
It would be advantageous if communication hardware could be developed that permitted flexibility in defining the frame synchronization byte structure, so as to permit the hardware to be used in a number of communication standards.
It would be advantageous if the number of frames with non-recognizable frame synchronization bytes (FSBs), required for synchronization to lapse could be made selectable in a multidimensional digital frame structure.
Likewise, it would be advantageous if the number, location, values, and bit error rates of the FSBs could be made selectable to accommodate a number of communication standards, or changes to existing standards.
Accordingly, an integrated circuit communication device is provided that includes programmable features that permit a user to allocate bandwidth for frame synchronization words, and set up error thresholding in adjusting the robustness to bit errors, and the time required to achieve synchronization. More specifically, the device provides for:
a programmable frame synchronization word bandwidth;
programmable frame synchronization words;
different synchronization words with independent allocated bandwidths;
frame synchronization word translation between the decoder and encoder;
frame synchronization word error thresholding for system robustness;
programmable synchronization (in-to-sync) parameters; and
programmable out-of-sync synchronization parameters.
Broadly, this invention describes a structure for programming key features in a frame synchronization system using a multidimensional digital frame. More particularly, an example of the invention is provided in a programmable framing structure for a forward error correction (FEC) encoded channel interleaved to 16 levels with a 4 frame superframe. The structure provides the user the ability to allocate the amount of bandwidth dedicated to the frame synchronization words, to control the speed of synchronization and the robustness to channel noise. As an added benefit, a programmable synchronization threshold can be set to even further increase the robustness to channel noise and to decrease the synchronization time under high bit error rate conditions. These techniques together allow users to increase network security and partitioning as well as to dynamically reallocate the bandwidth occupied for framing based on link conditions without corrupting user data.
Details of the programmable communication IC and a method for variably programming the frame synchronization structure in a multidimensional digital frame structure are provided below.